The clearance will allow the acquisition to proceed as soon as all other conditions to closing have been satisfied and it is expected to be finalised in mid-2011.

"We were very pleased to hear this positive news from the Department of Justice about this strategic acquisition," Caterpillar chairman and chief executive officer Doug Oberhelman said.

"Since we announced our plan to acquire Bucyrus last November, we have continued to hear from our customers that this complementary expansion of our mining product range is what they have been looking for from Caterpillar.

“This will position us to better serve the increasingly complex requirements of those customers."

The acquisition is based on Caterpillar's key strategic imperative to expand its leadership in the mining equipment industry and positions Caterpillar to capitalize on the robust long-term outlook for commodities driven by the trend of rapid growth in emerging markets which are improving infrastructure, rapidly developing urban areas and industrializing their economies, Oberhelman said.

Bucyrus president and chief executive officer Tim Sullivan said, "This is a critical and important step as we move toward closing this historic transaction that will deliver tremendous value to all the Bucyrus stakeholders."

Caterpillar will fund the acquisition through a combination of cash from its balance sheet and debt. Caterpillar does not plan to issue equity to help pay for the acquisition.